Vanadium garnet materials in the MnO-CaO-V2 O3 -SiO2 system

ABSTRACT

Vanadium garnet materials and a method for their preparation. The vanadium garnet material has a trivalent vanadium cation and a composition that falls within a specific prismatic-shaped volume in a quaternary composition diagram of MnO, CaO, V 2  O 3 , and SiO 2 . The prismatic-shaped volume represents compositions of liquids with which said vanadium garnet is in equilibrium on the liquidus surface and from which the vanadium garnet phase is crystallized. A typical vanadium garnet material has the formula Mn 1 .3 Ca 1 .7 V 2  Si 3  O 12 , as provided in the drawing by point F. The vanadium garnet materials may be used in laser applications.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to vanadium garnet materials in the MnO--CaO--V₂O₃ --SiO₂ system.

SUMMARY OF THE INVENTION

The present invention pertains to vanadium garnet materials and a methodfor their preparation. The material comprises vanadium garnet containingvanadium in the trivalent state. For example, point F in the drawingcorresponds to the formula Mn₁.3 Ca₁.7 V₂ Si₃ O₁₂ and falls within avolume of a quaternary composition diagram of MnO, CaO, V₂ O₃, and SiO₂.The material falling within said volume represents compositions ofliquids within the quaternary system MnO--CaO--V₂ O₃ --SiO₂ with whichsaid vanadium garnet phase is in equilibrium and from which the garnetphase is crystallized. The volume may be represented as a prism withvertices and corresponding coordinates in weight percent as shown inTable I.

                  TABLE I                                                         ______________________________________                                                 Coordinates (wt %)                                                   Vertices   MnO    CaO         V.sub.2 O.sub.3                                                                     SiO.sub.2                                 ______________________________________                                        A           1     41          45    13                                        B           1     49          32    18                                        C           1     44          17    38                                        D           1     25          27    47                                        E           1     36          48    15                                        A'         41      1          36    22                                        B'         49      1          25    25                                        C'         42      1          15    42                                        D'         22      1          32    45                                        E'         36      1          37    26                                        ______________________________________                                    

A method of preparing a vanadium garnet material in the MnO, CaO, V₂ O₃,and SiO₂ system, wherein said vanadium garnet is crystallized from amelt with which said vanadium garnet material is in equilibrium on theliquidus surface, and wherein the melt has a composition that fallswithin a prismatic-shaped volume ABCDEA'B'C'D'E' as shown in thedisclosed figure for a quaternary composition diagram of MnO, CaO, V₂O₃, and SiO₂ comprising the steps of:

(1) heating V₂ O₅ powder having a particle size of less than about 50microns in an atmosphere in which the partial pressure of oxygen is inthe range of 10⁻⁵ to 10⁻¹⁰ atmosphere and the CO₂ /H₂ volume ratio is inthe range of about 10/1 to 1/1 while gradually increasing thetemperature over a temperature range of about 600° C. to 1300° C. andholding the temperature at about 1300° C. for a period of at least about24 hrs. to ensure complete reduction of all vanadium to V³⁺ ;

(2) heating MnO, CaO, and SiO₂ powders each having a particle size ofless than about 50 microns for a period of about 10 to 14 hrs. at atemperature in the range of about 1000° C. to 1400° C.;

(3) thoroughly grinding together an amount of V₂ O₃ from (1) in therange of about 15 to 45 wt.%, with an amount of MnO from (2) in therange of about 1 to 49 wt.%, and an amount of CaO in the range of about1 to 49 wt.%, and an amount of SiO₂ from (2) in the range of about 13 to47 wt.% to produce a mixture having a grain size of less than about 50microns;

(4) pelletizing the mixture from (3) at a pressure of about 5,000 psi;

(5) heating the pellets from (4) at a temperature in the range of about1100° C. to 1400° C. for a period in the range of about 12 to 48 hrs. inan atmosphere in which the partial pressure of oxygen is in the range of10⁻¹⁰ to 10⁻⁵ atmosphere to produce a melt; and

(6) cooling the material from (5) and crystallizing out said vanadiumgarnet material, and separating said vanadium garnet material from therest of the melt.

BRIEF DESCRIPTION OF THE DRAWING

The drawing depicts a quaternary composition diagram of MnO, CaO, V₂ O₃,and SiO₂ showing a prismatic-shaped volume representing liquidcompositions which are in equilibrium with vanadium garnet material inthe liquidus volume and from which the vanadium garnet phase iscrystallized.

DESCRIPTION OF THE INVENTION

Vanadium garnet materials have been synthesized by the subject inventionin which garnet material involving trivalent vanadium cation as acomponent have been characterized. The garnet phases synthesized arethermodynamically stable over a wide range of oxygen pressures e.g.about 10⁻⁵ to 10⁻¹² atmospheres, and at elevated temperatures, e.g. upto about 1000° C.

The newly synthesized vanadium garnet materials produced fromMnO--CaO--V₂ O₃ --SiO₂ have compositions that fall within aprismatic-shaped volume in the quaternary composition diagram in thedrawing, wherein the prismatic-shaped volume represents compositions ofliquids with which said vanadium garnet is in equilibrium in theliquidus volume and from which said garnet phase is crystallized. Theoxidation state of vanadium in the garnet material is mainly +3.

The polygon shaped shaded area has the following vertices andcorresponding coordinates in weight percent:

    ______________________________________                                                 Coordinates (wt %)                                                   Vertices   MnO    CaO         V.sub.2 O.sub.3                                                                     SiO.sub.2                                 ______________________________________                                        A           1     41          45    13                                        B           1     49          32    18                                        C           1     44          17    38                                        D           1     25          27    47                                        E           1     36          48    15                                        A'         41      1          36    22                                        B'         49      1          25    25                                        C'         42      1          15    42                                        D'         22      1          32    45                                        E'         36      1          37    26                                        ______________________________________                                    

A typical newly synthesized vanadium garnet material having the formulaMn₁.3 Ca₁.7 Si₃ O₁₂ is illustrated by point F in the drawing having thefollowing coordinates in wt.%: MnO 19, CaO 19, V₂ O₃ 30, and SiO₂ 32. Itappears as beautiful euhedral crystals in equilibrium with liquids.

It is to be noted that the vanadium garnet appears as a primary phase inthe liquidus volume of the system, MnO--CaO--V₂ O₃ --SiO₂. Accordingly,the growing of single crystals of this material is relatively simple,provided that atmospheric control of the type used in the synthesisprocedure described herein is maintained during the crystal growingprocess. By the subject process, larger and better e.g. purervanadium-containing garnet crystals are grown. The size of thesecrystals are in the range of about 2 to 100 microns.

Quaternary compounds in the MnO--CaO--V₂ O₃ --SiO₂ system aresynthesized in the following manner. First, V₂ O₃ is prepared by heatingcommercially available analytical-grade V₂ O₅ having a particle size ofless than about 50 microns in a vertical tube furnace in an atmosphereof carefully selected oxygen pressure within the stability range of V₂O₃ e.g. in the range of 10⁻⁵ to 10⁻¹⁰ atmospheres. This is accomplishedby using a gas mixture of high-purity CO₂ and H₂ in controlledproportions. The CO₂ /H₂ ratio by volume is in the range of 10/1 to 1/1.The relatively low melting point of the starting vanadium oxide (V₂ O₅),e.g. about 690° C., necessitates heating the oxide slowly. Starting at atemperature of about 600° C., the temperature is gradually increasedover a period of about 12 to 24 hrs. to a final temperature of about1300° C. At a temperature of about 1300° C. the vanadium oxide is heldat least about 24 hrs. e.g. 24 to 30 hrs. to ensure complete reductionof all vanadium to V³⁺ (V₂ O₃).

Pre-heated analytical-grade oxides having a particle size of less thanabout 50 microns are used as starting materials for the other componentsof the garnet phase to be synthesized. For example, MnO, CaO and SiO₂are heated for about 10 to 14 hrs. at a temperature in the range ofabout 1000° C. to 1400° C. prior to being used in preparation of thefinal mixtures.

The mixtures of the four oxide components are mechanically groundtogether under acetone in an agate mortar to ensure thorough mixing anda sufficiently small grain size e.g. less than 50 microns. For example,a specific amount of V₂ O₃ in the range of about 15 to 45 wt.% is groundtogether with MnO in the range of about 1 to 49 wt.%, and an amount ofCaO in the range of about 1 to 49 wt.%, and SiO₂ in the range of about13 to 47 wt.% to produce a mixture having a grain size of less thanabout 50 microns. Complete formation of the desired compounds in theheat treatment step is thereby promoted. The oxide mixtures arepelletized at a pressure of about 5,000 psi or higher. The pellets mayhave any conventional size e.g. 1/16"to 1". The pellets are then heatedat a temperature in the range of about 1100° C. to 1400° C. for a periodin the range of about 12 to 48 hrs. in a vertical tube furnace withcarefully controlled oxygen pressures, and in the range of 10⁻¹⁰ to 10⁻⁵atmosphere to produce a melt. In the manner described previously forpreparing V₂ O₃, the pellets are heated in a furnace atmosphere providedby a gas mixture of CO₂ and H₂ in various desired mixing ratios,typically in the range of about 10/1 to 1/1. These selected ratios arekept constant for the duration of the synthesis by use of a differentialmanometer. By this method the oxygen pressure at the specifiedtemperature can be controlled to better than ±1%. The thermodynamic datafor the water-gas reaction (CO₂ +H₂ = CO+H₂ O), on which thecalculations were based, are known with extremely high accuracy (betterthan 0.1%), and hence the method used ensures reliable accurate controlof the oxidation state of vanadium during the synthesis. This isextremely important for optimization of the properties of the finishedproduct.

The molten material from the furnace is cooled to a temperature which isabove the freezing point of the rest of the melt e.g., above about 1100°C. The cooling takes place over a period in the range of about 1 to 12hours while at substantially the same partial pressure of oxygen as thatin the furnace. The vanadium garnet material will thereby crystallizeout from the melt and may be separated by conventional means from therest of the liquid melt, such as by decanting. The identity of thestable solid compositions produced from MnO--CaO--V₂ O₃ --SiO₂ may beconfirmed by x-ray diffraction analysis.

The vanadium garnet material involving MnO--CaO--V₂ O₃ --SiO₂ may beused in laser applications, offering greater stability over a widertemperature range e.g. about 1000° C. or higher than that which isoffered by typical laser materials.

Various modifications of the invention as herein before set forth may bemade without departing from the spirit and scope thereof, and therefore,only such limitations should be made as are indicated in the appendedclaims.

We claim:
 1. A vanadium garnet material in the MnO--CaO--V₂ O₃ --SiO₂system, wherein the volume circumscribed by ABCDEA'B'C'D'E' as shown inthe disclosed Figure for a quaternary composition diagram of MnO, CaO,V₂ O₃, and SiO₂ represents compositions of liquids with which saidvanadium garnet is in equilibrium in the liquidus volume and from whichsaid vanadium garnet material is crystallized, and wherein the amountsof MnO, CaO, V₂ O₃, and SiO₂ are characterized as shown in the tablebelow:

    ______________________________________                                                 Coordinates (wt %)                                                   Vertices   MnO    CaO         V.sub.2 O.sub.3                                                                     SiO.sub.2                                 ______________________________________                                        A           1     41          45    13                                        B           1     49          32    18                                        C           1     44          17    38                                        D           1     25          27    47                                        E           1     36          48    15                                        A'         41      1          36    22                                        B'         49      1          25    25                                        C'         42      1          15    42                                        D'         22      1          32    45                                        E'         36      1          37    
 26.                                      ______________________________________                                    


2. A vanadium garnet material as provided in claim 1 having the formulaMn₁.3 Ca₁.7 V₂ Si₃ O₁₂ as illustrated by point F in said quaternarycomposition diagram and having the following coordinates in wt.%: MnO19, CaO 19, V₂ O₃ 30, and SiO₂
 32. 3. A laser material in theMnO--CaO--V₂ O₃ --SiO₂ system, wherein the volume circumscribed byABCDEA'B'C'D'E' as shown in the disclosed Figure represents compositionsof liquids with which said laser material is in equilibrium in theliquidus volume and from which said laser material is crystallized, andwherein the amounts of MnO, CaO, V₂ O₃, and SiO₂ are characterized asshown in the table below:

    ______________________________________                                                 Coordinates (wt %)                                                   Vertices   MnO    CaO         V.sub.2 O.sub.3                                                                     SiO.sub.2                                 ______________________________________                                        A           1     41          45    13                                        B           1     49          32    18                                        C           1     44          17    38                                        D           1     25          27    47                                        E           1     37          49    15                                        A'         41      1          36    22                                        B'         49      1          25    25                                        C'         42      1          15    42                                        D'         22      1          32    45                                        E'         36      1          37   
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